Table 1.

BMP pathway gene deletion: animal model phenotypes

Gene	Global deletion phenotype* (mouse except where stated zebrafish)	Endothelial cell-selective deletion phenotype (mouse except where stated zebrafish)
Bmp2	Embryo: Lethal (E7.5–10.5); Failed closure of pro-amniotic canal; malformed amnion/chorion, cardiac development defects [232]	Adult (Tie2-Cre): Hemochromatosis (serum and tissue iron overload), ↓ spleen iron [33, 233] Adult (Cdh5-Cre): Viable; no vascular phenotype reported [234, 235]
Bmp4	Embryo: Lethal (E6.5-E9.5); Defective mesoderm differentiation and blood island formation [31]	Adult (Cdh5-CreERT2) (Excised at 6–8weeks and challenged with thioglycolate): Diminished leukocyte infiltration in acute inflammation [146]
Bmp6	Embryo: (Late gestation) ossification delay [236] Adult: Viable, fertile, no overt defects, normal ossification in pups/adults [236] Adult: Hemochromatosis (serum and tissue iron overload), ↓spleen iron [32, 33]	Adult (Tie2-Cre): Hemochromatosis (serum and tissue iron overload), ↓ spleen iron [32, 33]
Bmp9	Late Embryo/Neonate: Disrupted lymphatic development (↑ LEC proliferation/enlarged lymph vessels, ↓ lymphatic valves) [25, 26] Post-Natal Retina: Viable; Normal vascular development. With BMP10 neutralizing antibody: ↑ vascular density and ↓ vascular expansion [24, 28] Zebrafish embryo (morpholino): Venous remodeling defects [27] Zebrafish embryo (mutant): Viable; no overt phenotype [30]	N/A
Bmp10	Embryo: Lethal (E10.0–10.5); ↓ cardiomyocyte proliferation (arrested cardiogenesis), ventricular hypoplasia, ↓ ventricular trabeculae (impaired trabeculation), abnormal endocardial cushion development, severely impaired cardiac function and circulation, vascular impairment [37]. Developmental arrest at E10.5, enlarged pericardium, AVM (DA and CV dilated and fused into single continuous channel), yolk sac: no vitelline vessels and stalled primary capillary plexus development [28] Zebrafish embryo (morpholino bmp10 + bmp10-like double KD): AVMs in midbrain and hindbrain; enlarged cranial basal communicating artery [29] Zebrafish embryo (mutant, bmp10 + bmp10-like double KO): Lethal high-flow cranial AVMs [30] Zebrafish juvenile/adult (mutant bmp10): Premature death, abdominal edema, enlarged/hemorrhagic skin blood vessels, disorganized liver vasculature, high-output heart failure [30]	N/A
Bmpr2	Embryo: Lethal (< E9.5); Pre-gastrulation developmental arrest, lack primitive streak and mesoderm [87] Embryo: (Mox2-Cre) Gastrulation and mesoderm defects, cardiac defects including double-outlet right ventricle (DORV), ventricular septal defect (VSD), AV cushion defects, thickened valve leaflets [237] Adult (Bmpr2+/−): ↑ mean arterial pressure and pulmonary vascular resistance; thickened muscularized pulmonary artery walls; ↑ alveolar-capillary units; mild pulmonary hypertension; impaired pulmonary vascular remodeling [171] Adult (Bmpr2+/−;ApoE−/−): Accelerated atherosclerosis and ↑ endothelial inflammation in arteries [221]	Embryo (Tie2-Cre): AV cushion defects (atrial septal defect, membranous VSD, thickened valve leaflets) [237] Neonate (Tie2-Cre): Lethal (~ P7); Abnormal AV cushion remodeling, thickened semilunar valve formation [237] Post-Natal Retina (Cdh5-CreERT2): ↓ radial expansion, ↓ vascular density, and ↓ sprouting at angiogenic front [59] Adult (Alk1-Cre-L1, pulmonary EC): Predisposition to develop PAH (elevated right ventricular systolic pressure (RVSP)) associated with right ventricular hypertrophy and ↑ number and wall thickness of distal pulmonary arteries [172]. ↑ leaky pulmonary vessels, ↑ leukocyte infiltration into lungs [173] Adult (Tie2-rtTA x TetO7-Bmpr2delx4): ↑ RVSP; muscularization of small vessels; thrombosis, ↑ inflammatory cells, ↑ proliferating cells, moderate ↑ in apoptotic cells [238] Adult (Scl-CreERT, general EC): RVSP under hypoxic conditions (measure of PAH) [83]
Alk1	Embryo: Lethal (E10.5); Excessive capillary plexus fusion; impaired yolk-sac/embryonic vascular development; large vessel dilation; VSMC differentiation and recruitment defects [218]. AVMs between DA and CV by E8.5, and in multiple areas by E9.5 [191] Post-Natal Retina (Rosa26-CreER): (Excised at P3) Extensive, fully dilated AVMs at P5 [184] Neonate (Rosa26-CreERT2): ↑ density, ↑ # filopodia, and ↑ diameter of lymphatic vessels of various tissues. Blood vessels not assessed [26] Adult (Rosa26-CreER): Sex-dependent lethality 9–21 days post-excision. ↓ weight and hemoglobin levels, ↑ hemorrhage and anemia, enlarged heart, dilated pulmonary arteries and veins, AVMs in gastrointestinal tract, uterus, and wounded skin [184, 219] Zebrafish embryo (mutant alk1y6): Dilated high-flow cranial AVMs, ↑ number of endothelial cells in cranial vessels due to directed arterial EC migration [193]. Edema in head, pericardium, and yolk sac [194] Zebrafish embryo (morpholino alk1): Cerebral AVMs by 24 hpf, high-output heart failure by 3–4 dpf [196]	**Embryo (Alk1-Cre-L1, pulmonary EC): Lethal (E17.5); AVMs and dilated/tortuous vitelline arteries in E16.5 extraembryonic vasculature, and AVMs in E17.5 lung vasculature [239] **Neonate (Alk1-Cre-L1, pulmonary EC): Lethal (P5); Dilated, disorganized, tortuous blood vessels causing hemorrhage in brain/lung/small intestine. AVM shunts in brain and lungs [219] Neonate (Cdh5-CreERT2): Lethal ≤ 48 h following excision. Pulmonary hemorrhage, AVMs in pial vessels and GI tract [166, 168] Post-Natal Retina (Cdh5-CreERT2): Venous enlargement, vascular hyperbranching, ↑ vascular density, ↑ filopodia density, ↑ EC proliferation, AVMs, loss of arterial identity, ↓ pericyte coverage, ↓ pSMAD1/5/8 activity, ↓ endoglin expression [59, 166–168] Adult (Cdh5-CreERT2): Severe GI bleeding due to fragile microvessels in cecum villi, ↓ oxygen saturation due to hemorrhage, ↓ hematocrit and hemoglobin levels) [168] Adult (Scl-CreERT general EC): Lethal ~ 2 weeks following excision. AVM shunts (tortuous, enlarged vessels) in ear, GI tract, and skin wound areas. Severe cecal hemorrhage, fatal anemia. No effect on lymphatic vessels [227] Overexpression (Alk1-Cre-L1, Scl-CreERT, and RosaCreER): No pathological symptoms alone. Suppressed formation of AVMs in postnatal retinas and adult wounded skin in Alk1iECKO and EngiECKO mice [192]
Alk2	Embryo: Lethal (< E9.5); Defects in mesoderm formation & gastrulation (abnormally thickened primitive streak, arrested development at late streak stage) [240, 241]. Arrested at early gastrulation stage, abnormal visceral endoderm morphology and severe disruption of mesoderm formation [242]	Embryo (Tie2-Cre): ↓ endocardial cushion size at E10.5, defects in heart septation and valve formation at E14.5, failure to undergo EndoMT [243] Post-Natal Retina (Cdh5-CreERT2): ↓ radial expansion and vascular density [59]
Alk3	Embryo: Lethal (< E9.5); No mesoderm formation, no gastrulation, thickened epiblast layer [244] Zebrafish embryo (morpholino, alk3a/b): ↓ Ephb4 expression, only one axial vessel present, lack of proper blood circulation [185] Adult (Alk3+/−): Normal, viable, fertile [244]	Embryo (Flk1-Cre): Lethal (E10.5–11.5); Defects in vessel remodeling and smooth muscle cell formation/recruitment, severe abdominal hemorrhage, AV canal endocardial cushion defects (↓ proliferation), anemic yolk sacs [226] Embryo (Tie1-Cre): Lethal (E11.5–12.5); Internal hemorrhage, ↓ mesenchymal AV cushion cells at E9.5–10.5, impaired EMT in AV canal [245] Embryo (Tie2-Cre): Lethal (E10.5); Severe growth retardation, lack of venous vessels, ↓ SMCs around dorsal aorta [185] Embryo (Dll4in3-Cre, arterial EC): No overt phenotypes [185] Post-Natal Retina (Cdh5-CreERT2): ↓ radial expansion, ↓ vascular density, ↓ sprouting at the angiogenic front [59]
Alk6	Embryo: Failure of metacarpals to segment, ↓ cell proliferation and ↑ cell death in digit regions [246] Neonate: Defects in appendicular skeleton (impaired chondrogenesis in proximal and middle phalanges region) [61] Adult: Viable; Defects in appendicular skeleton [61, 246]. Fertilization difficulty, irregular estrous cycle [247]	N/A
Smad1/5/9	Embryo (Smad1−/−): Lethal (E9.5); Impaired allantois formation, lack of placenta, disorganized vessels, lack of embryonic circulation [248, 249] Embryo (Smad5−/−): Lethal (E9.5–11.5); Impaired vasculogenesis and hematopoiesis, disorganized yolk sac vasculature, edema, hemorrhage in amnion, exteriorized heart, failure to close mid/hindgut and neural tubes [250]. Vascular development defects: enlarged blood vessels, fewer vascular smooth muscle cells, ↑ apoptosis of mesenchymal cells [251] Embryo (Smad9−/−): No overt defects; adults viable and fertile [252] Embryo (Smad1+/−;Smad5+/−): Lethal (E10.5); Impaired allantois morphogenesis, cardiac looping, and primordial germ cell specification [252] Zebrafish embryo (morpholino, smad1/5): ↓ Ephb4 expression [185] Adult (Smad9LacZ−/−, aged 11.5 months): Lung vascular remodeling defects (media hyperplasia with vessel occlusion and plexiform lesions). A subset of mutants developed pulmonary adenomas. Heterozygotes: similar but milder phenotypes at a lower prevalence [253]	Embryo (Smad1f/f; Smad5f/f; Tie2-Cre): Lethal (E10.5); Severe vascular hemorrhage and edema, normal vasculogenesis but impaired angiogenesis, ↓ Dll4/Notch signaling, ↑ tip-cell-like cells (at expense of stalk cells) in E9.5 hindbrain and dorsal aorta but ↓ anastomoses of sprouts [228]. Spontaneous vascular shunt formation (AVM-like) between heart and dorsal aorta in yolk sacs at E9.25 [212] Post-Natal Retina (Cdh5-CreERT2): AVMs in high flow areas, ↓ functional tip cells at angiogenic front, ↑ vascular density in plexus, ↓ vessel regression, aberrant vascular loop formation [165]
Smad4	Embryo: Lethal (E6.5–8.5); Arrested growth before gastrulation due to ↓ cell proliferation, no mesoderm formation, abnormal visceral endoderm [254, 255] Embryo (Rosa-CreER): (Excised at E10.5) Disrupted arterial development, dilated coronary arteries, ↑ arterial EC size and proliferation. (Excised at E15.5) no change in vessel diameter [217] Neonate (Rosa-CreER): (Excised at P1) Lethal by P8, GI hemorrhage, dilated and tortuous AVMs in brain, intestine, nose, and retina [184] Post-Natal Retina (Rosa-CreER): (Excised at P1) AVM formation, aberrant smooth muscle actin staining, ↓ radial expansion [184] Adult (Rosa-CreER): Lethal ≤ 6 days of excision. ↓ weight and hemoglobin levels, GI hemorrhage, enlarged stomach/intestine/cecum, dilated and tortuous AVMs along GI tract and wounded skin [184]	Embryo (Flk1-Cre): Lethal (E9.5–10.5); ↓ hematopoietic colonies [226] Embryo (Tie2-Cre): Lethal (E9.5–10.5); Growth retardation, defects in vessel sprouting and remodeling, collapsed dorsal aortas, enlarged hearts with ↓ trabeculae, failed endocardial cushion formation, lack of Ephb4 expression and absence of cardinal vein [185, 256] Embryo (Cdh5-CreERT2): (Excised at E9.5) Lethal (E13.5); Defective vein morphology, ↓ Ephb4 expression [185] Embryo (Dll4in3-Cre, arterial EC): No overt phenotypes in embryos before E13.5, but lethal between E13.5 and P5 [185] Embryo (Apj-CreER, venous-derived EC): (Excised at E10.5) Dilated coronary arteries [217] Neonate (Cdh5-CreERT2): Lethal 4–8 days following excision. Defective lung vasculature and lung hemorrhage causing respiratory distress, AVMs in pial vessels and GI tract [166] Post-Natal Retina (Cdh5-CreERT2): AVM formation (in 82% of mutants), angiogenic defects, arteriovenous identity issues, ↑ artery/vein diameter, ↑ EC proliferation and size, altered mural cell coverage, ↓ Vegfr2 expression [183]. AVMs, ↑ vascular density and branchpoints at vascular front, ↑ EC proliferation in branching plexus, arteriovenous identity defects [166]
Smad6	Background-dependent, variable late-embryonic/perinatal lethality [257, 258] Embryo: Hemorrhage under skin [145]. Axial and appendicular skeletal defects [258] Neonate: Hyperplastic endocardial cushions, variable valve and outflow tract septation defects[257]. Domed skulls and short snouts [258] Post-Natal Retina: ↑ sprouting at the vascular front, ↑ density in branching plexus, disorganized EC junction markers [145] Adult: Ossification around outflow tracts of heart [257]	N/A
Smad7	Embryo: Significant postnatal lethality with cardiac defects: VSD, non-compaction; outflow tract (may result from elevated TFGb signaling) [259] Adult: small size, abnormal ECG, thin ventricular wall [259]	N/A
Endoglin	Embryo: Lethal (E10.0–11.5); Defective yolk sac vasculogenesis, embryonic angiogenesis, and vascular smooth muscle cell development; hemorrhage in yolk sac and embryo, cardiac malformations (enlarged ventricles and outflow tracts), cardiac cushion defects (failure to undergo EMT), delayed maturation of major vessels, severe anemia and ↓ red blood cell count [260–262] Adult (Rosa-CreER): ↓ weight and hemoglobin levels, GI hemorrhage, dilated and tortuous AVMs along GI tract and wounded skin [184]. AVM formation in brain following local VEGF stimulation [263] Adult (Eng+/−): Viable and fertile. Background-dependent and variable penetrance of telangiectases and dilated/tortuous vessels in skin, low frequency of AVMs [261, 262] Zebrafish embryo (mutant engmu130): ↓ blood flow through ISVs, altered blood vessel diameters bypassing smaller ISVs to shunt through large arteries and veins, ↑ blood vessel pruning [220] Zebrafish adult (mutant engmu130): Survive to adulthood. Multiple vascular malformations, dilated/tortuous vessels in head, ↑ artery and vein diameter, but ↑ EC numbers in veins only [220]	Neonate (Cdh5-CreERT2): (Excised at P1) AVMs and ↑ tip cells in brain [169] Post-Natal Retina (Cdh5-CreERT2): Vascular hypersprouting, delayed capillary remodeling, severe AVM formation (20% of those were bleeding AVMs), αSMA expression no longer follows arteries specifically and is found on veins too, ↑ vessel branching at periphery, enlarged veins, ↑ EC proliferation [169, 170] Post-Natal Retina (Apj-CreERT2): AVMs in proximal and distal retina [264] Adult (Cdh5-CreERT2): ↓ angiogenesis and venomegaly (matrigel plug assay) [170] Adult (Scl-CreERT, general EC): Dilated/tortuous vessels and arteriovenous shunts in wounded skin [227] Adult (Sm22α-Cre): Lethal ~ 6 weeks of age. AVM formation in brain, spinal cord, and intestines, hemorrhage in some brain and spinal cord lesions [263]

E10.5 embryonic day 10.5, P5 postnatal day 5, LEC lymphatic endothelial cells, AVM arteriovenous malformation, DA dorsal aorta, CV cardinal vein, DORV double-outlet right ventricle, VSD ventricular septal defect, AV atrioventricular, PAH pulmonary arterial hypertension, RVSP right ventricular systolic pressure, VSMC/SMC (vascular) smooth muscle cell, hpf/dpf hours (days) post-fertilization, GI gastrointestinal, EC endothelial cell, EndoMT endothelial-to-mesenchymal transition, EMT epithelial-to-mesenchymal transition

*Global mutant phenotypes may not be discussed in the text, but are included in Table 1 for comparison to endothelial-specific mutant phenotypes

**Divergent timing of similar phenotypes in Alk1f/f;Alk1-Cre-L1 mice attributed to different Cre-mediated recombination efficiencies